Diesel engine includes a Diesel Particulate Filter (DPF) in an exhaust pipe thereof in order to remove particulate matters (PM) contained in exhaust gas. The DPF is configured to collect PM such as soot in the exhaust gas and discharge PM-reduced exhaust gas to an outside. Increase in the amount of PM collected by the DPF results in deterioration of filter function. Accordingly, a regeneration processing for combusting the collected PM is performed in the DPF.
The regeneration of the DPF includes: a natural regeneration, in which the deposited PM is naturally combusted when the temperature of the exhaust gas is high; and a forced regeneration performed when the PM deposition amount exceeds a predetermined reference value. In the forced regeneration of DPF, operating conditions of an engine is controlled to raise the exhaust temperature and an external dosing in which fuel is injected in an upstream of the DPF or an internal dosing in which the fuel is injected into a cylinder of the engine is performed, thereby forcibly combusting the deposited PM.
Since the PM deposition amount collected by the DPF cannot be actually measured during an operation of the engine, the PM deposition amount is estimated by calculation. Typically, the PM deposition amount is calculated based on a differential pressure detected between an exhaust gas inlet and exhaust gas outlet of DPF. Then, when the PM deposition amount exceeds a predetermined amount, the forced regeneration is performed.
However, as shown in FIG. 14, though collected PM 101 uniformly deposits in cell of the DPF, the PM 101 deposited in the cell is partially peeled off as more amount of the PM 101 is deposited, and peeled PM 102 may sometimes clog the cell. The cell clogging increases the differential pressure in the DPF, and a forced regeneration may be sometimes performed even when the actual PM deposition amount is not at a level requiring the forced regeneration.
In view of the above, Patent Literature 1 discloses that a PM amount deposited in a DPF is estimated using a model in which the PM amount combusted in the DPF is subtracted from the PM amount in the exhaust gas received by the DPF, and the forced regeneration processing is performed using the estimated PM amount deposited in the DPF.
Patent Literature 2 discloses that the forced regeneration processing of a DPF is performed when a reduction rate of the differential pressure in the DPF reaches a predetermined value or more.